Joint for the transmission of motion from a driving shaft to a driven shaft

ABSTRACT

Elastic joint for the transmission of motion between two shafts, comprising two supports, a driving support and a driven support, associated with the shafts and at least two arms for each support. The joint comprises at least one single element for connecting the two arms, this element being in the form of a closed annular strap of inextensible and flexible material. The strap can be disposed on a plane separating the two supports at a position substantially central to the joint so as to form a polygon whose vertices are the ends of the arms belonging alternatively to the driving support and driven support.

DESCRIPTION

The present invention is directed to a joint for the transmission of motion between a driving shaft and a driven shaft and, more precisely and among other things, to a joint of the elastic type.

As known, an elastic joint must do the following tasks:

(a) to allow the connected shafts to undergo relative inclinations;

(b) to permit small relative parallel movements;

(c) to permit a limited variety of relative axial movements;

(d) to permit relative rotations of the two shafts on varying of the transmitted torque, in order to transmit sudden load variations from the driving shaft to the driven shaft in an attenuated manner.

According to one example, an elastic joint can be constituted by a polygonal element formed by rubber blocks, where each polygonal element is provided with bushings at its ends; in this case, the driving shaft and the driven shaft are connected alternatively to the bushings inserted in the rubber polygonal elements.

This type of joint and other like joints based substantially on the use of elastomeric material are adapted, for instance, to realize a power transmission between a driving shaft and a driven shaft graduating the torques and the torque variations from the driving shaft with respect to the driven shaft through a variation of the condition of deformation of the blocks of elastomeric material, such as of rubber.

According to another solution, an elastic joint is constituted mainly by a rubber disc provided with bushings for the passage of the bolts of two spiders connected respectively to the driving shaft and to the driven shaft. Each bushing is connected to each one of the adjacent bushings through a grommet embedded in the disc rubber; preferably, said grommet is folded upon itself so as to take an eight-like shape.

This solution can produce, in some cases, the drawback of an insufficient covering of the grommet with elastomeric material, and further the drawbacks of a complicated and laborious step for assembling the various elements forming the joint. Then, it is to be noted, that the cited solutions can cause high hysteretic losses owing to the presence of the elastomeric material having a considerable thickness, with the consequence of reducing the value of the useful power to be transmitted between driving shaft and driven shaft--especially in the case of marked misalignment between the shafts.

Therefore, the present invention aims at providing a joint for the transmission of motion between a driving shaft and a driven shaft that is adapted to satisfy the requisites of the elastic joints, and at the same time which is constituted by the smallest possible number of useful elements for the transmission of motion between the driving and driven shafts, and which therefore is of easy and rapid assembly so as to be manufactured on an industrial scale at low cost and at high efficiency in the power transmission.

The object of the present invention is a joint for the transmission of motion from a driving shaft rotating around a first axis to a driven shaft rotating around a second axis, said joint comprising two supports, one driving and one driven, associated with said shafts, each support comprising at least two arms, said joint being characterized by comprising at least one single element for the connection between the arms for the transmission of motion between the shafts constituted in the form of a closed annular strap of flexible material and resistant to traction, said strap being arranged on a plane separating the two supports, at a central position with respect to the joint so as to form a polygon whose vertices are the ends of the arms belonging aternatively to the driven and driving supports and whose sides constitute tension rods for the transmission of motion between the driven shaft and the driving shaft, said tension rods being during the operation equal to half of the polygon sides, following alternatively sides under traction and inactive sides and the traction condition exchanging with the inactivity condition on varying the sign of the transmitted torque.

The present invention will be still better understood by the following detailed description made by way of non-limiting example with reference to the figures of the attached sheets of drawing, in which:

FIG. 1 is a perspective view of the part relating to the supports of a joint according to the present invention in the form of two arms for each support, in which the polygon enveloping the element for the connection between the supports is shown schematically by a broken line;

FIG. 2 shows, in a front view according to the arrow F₁ of FIG. 1, a complete view of the joint comprising the connecting element in the form of a polygon connecting arms belonging alternatively to the driven and driving supports;

FIG. 3 is a perspective view of the joint;

FIG. 4 is a perspective view of a strap, in the manufactured shape as cylindrical ring, adapted for the formation of the polygonal system of the tension rods of FIG. 2;

FIG. 5 is a perspective view of the arrangement of the strap represented in FIG. 4 at the ends of the arms of the supports;

FIG. 6 shows the end of the arms of the supports after the assembling of the annular element of FIG. 4;

FIG. 7 shows in perspective view the scheme of the supports for an alternative embodiment of the joint with constant angular velocity according to the invention;

FIG. 8 shows some details of the supports of FIG. 6 according to some embodiments;

FIGS. 9 to 13 show the operations for transforming a strap in the form of a ring into a polygonal system whose sides constitute the tension rods of the joint according to the invention;

FIG. 14 is a partial view of a hexagonal polygonal system of tension rods adapted to constitute the system of tension rods for a joint according to the invention; and

FIG. 15 shows the outer development of the polygonal joint to determine the tube adapted for manufacturing a plurality of cylindrical annular straps for various joints according to the invention.

FIGS. 1 to 3 represent a joint 1 for the transmission of motion from a driving shaft rotating around an axis X--X to a driven shaft rotating around an axis Y--Y.

The joint 1 comprises two supports 2, 3 (in the embodiment of FIG. 1 in a flat shape), a driving support and a driven support, respectively, defined by middle planes being perpendicular to one another and, in one possible embodiment, a single continuous element 4 for the transmission of motion from one support to the other.

Each support is made of a rigid material, for instance steel, and comprises two parts, here called arms, aligned to one another and indicated in FIG. 1 by 5, 6, 7, 8, respectively.

In the present description, as a single element adapted for the transmission, there is indicated a continuous element in the form of a cylindrical ring or sleeve of flexible material and resistant to traction, for instance a thin strap of elastomeric material embedding reinforcing elongated elements, as for instance threads, filaments, textile and metallic cords.

The annular strap is disposed between the supports (FIG. 2) so as to form a sequence of sides 4' in that Figure, connecting to one another alternatively the ends of the arms of the driving support with the ends of the arms of the driven support to constitute thus a polygonal system of useful tension rods for the transmission of motion between the shafts.

The application of the strap to determine the system of tension rods constitutes a particularly advantageous and essential characteristic of the invention. In fact, it is possible to determine the connection between the two supports, with only the strap obtained by easy manufacturing processes; the whose without cutting the strap itself into various segments in a number equal to the tension rods in order to then connect and block them to the bearing structure of the joint.

In this connection, the joint comprises means for coupling and blocking the annular strap at the end of each arm.

In a preferred embodiment, said means for blocking and coupling the strap to the joint structure are obtained, as schematically shown in FIG. 5, relating to the connection of the strap with one of the ends of any of the two joint supports.

In practice the strap 4, shown in FIG. 4 in its original shape, is folded upon itself so as to form a folding edge 9 from which two sides project. Then, the two sides of the strap are placed under rotation around the second edges 10 and 11 in a plane substantially perpendicular to the overlapping plane (FIG. 5).

The angle of inclination α between the edge 9 and the edge 10 and between the edge 9 and the edge 11 is substantially 45°.

Thus, there is obtained a part 12 of the strap formed substantially by two equal right-angled triangles having one common side formed by the connecting edge 9.

Then, the portion 12 of the strap, formed by the two cited equal triangles, is fitted around the chamfer at the end 13 of the support illustrated in the underlying position of FIG. 5.

In a further assembling step, two rigid elements, e.g., plates 14, 15, of equal shape are associated with the support so as to clamp the chamfering part of the support and the strap fitting around said chamfering part.

The blocking of the lateral portion of the strap is subsequently made permanent by the fact that the two rigid elements shaped, in one embodiment, as two plates 14, 15 (FIGS. 2, 6). Plates 14, 15 are tightened together by nut and bolt systems, which are shown schematically by the lines 16, 17 in FIG. 2. The bolts pass to a zone outside the run of the annular strap around the support chamfer in a suitable way.

As shown in FIG. 2, the joint is practically formed by a quadrilateral, with sides a, b, c, d whose resistance to traction permits the transmission of motion between the two supports 2 and 3, and therefore between the driving shaft and the driven shaft.

The system of tension rods forming the quadrilateral obtained by following the construction visible in FIGS. 4 to 6 lies completely on a single plane of separation between the supports 2 and 3.

In the transmission of motion, when the torque is transmitted from one shaft to the other in a given direction, the opposite sides a and c will act under traction, while the opposite sides b and d will act for the torque transmitted in the opposite direction.

The joint 1 further comprises means for avoiding mechanical interferences between the portions of the supports 2 and 3 in the movement such that the two driving and driven shafts would otherwise suffer during operation. Said means are in the form of grooves 18 and 19 (FIG. 1) at the center of the supports in order to avoid possible mechanical interference owing to relative movement between the driving and driven shafts coming too close together.

The joint according to the invention can also be constructed according to alternative embodiments, which permit one to obtain a homokinetic transmission between the driving shaft and the driven shaft. Said alternative embodiments comprise, in practice, two coupled joints, each of which is equal to that of FIG. 1, with the difference that the two supports facing the middle part are in a single intermediate rigid support.

In particular, according to one embodiment, the supporting elements of the joint, with constant velocity according to the invention, are represented in FIG. 7 in the condition of aligned driving and driven shafts and comprise two end supports 20 and 21, whose middle sections lie in alignment on a single plane and a rigid support 22 whose middle section lies on a plane perpendicular to the plane of the two end supports.

In this case, the intermediate support comprises two forks 23, 24 for the polygonal windings, and two central grooves 25, 26 to avoid mechanical interference.

On the whole, the joint makes use of two annular elements which form two polygonal systems of tension rods, completely comparable to those already represented in the previous figures.

Two blocking plates 27 act on the intermediate support, one of said plates being represented in FIG. 8. The plate 27 is provided with holes 28 suitable for receiving screws for blocking the windings of the strap which involve the forks of the intermediate support.

The invention comprises further embodiments of the joint, in particular, in respect of the formation of the single or double annular element for the connection between the driving support and the driven support

By way of example, some embodiments are shown schematically in FIGS. 9 to 13, which, for the sake of clearness, illustrate the coupling system between annular elements, and supports are described separately according to a sequence. As shown, said coupling is effected by starting from an annular element formed by a strap 30, such as that of FIG. 9, and originates in an automatic manner the assembling steps of the joint.

The assembling steps of the single connecting element between the joint supports, according to the present invention, may be carried out as follows:

four equally spaced edges are defined along the ring, for instance, in this way:

the cylindrical strap 30 is folded so that the area enclosed by its contour is nullified or reduced, obtaining thus two folding edges 31, 32, as shown in FIG. 10;

the strap is expanded again and the step is repeated, forming two new edges 33 and 34 (FIG. 11) so that the two edges 31 and 32 face each other. In this way, there is obtained in practice a quadrilateral with four equal sides, as shown in the top perspective view of FIG. 11.

Next, the zones adjacent to said edges are prepared for being coupled with the supporting elements. Said transformation is shown in respect of the edge 33 to which the sides 35 and 36 of the annular element converge.

The transformation is carried out with the following steps which, for sake of simplicity, are referred to an angle (FIG. 5) of 45°:

at first, a further edge 37 is formed on two sides of the strap, forming an angle of 45° with the edge 33 (FIG. 11) and forming a right-angled triangle at the end of the annular element;

the step for the formation of further edges 38, 39, 40, inclined at 45° with respect to the edges of FIG. 11 indicated with 32, 34, 31, respectively, is repeated;

at this point, the portions 35 and 36 referred to the edge 33 (FIG. 12) are laid, and likewise the other portions of the annular elements are laid on one and the same plane so as to obtain the four branches for the connection with the arms of the supports, as represented in FIG. 13.

The triangular portions formed at the vertex zone of the quadrilateral of FIG. 13 result in being arranged on perpendicular planes to the plane of the figure, intersecting said plane according to the edges 37, 38, 39 and 40 of FIG. 13.

Then, there is obtained the transformation of the cylindrical sleeve of FIG. 9 into a coplanar system of sides of a quadrilateral, as shown in FIG. 13, and thereby forming the continuous element of connection with the arms of the driving and driven supports.

This polygonal system has four triangular zones which, in FIG. 13, are called A, B, A₁, B₁.

The joint is obtained by fixing the opposite triangular portions A and A₁ to a support, for instance for driving support, and the triangular portions B and B₁ on the second support, at 90° with respect to the first one.

The portions A and A₁ may be above the plane of FIG. 13, and the portions B and B₁ below the same plane in order to facilitate the connection to the supports.

The anchoring of the triangular portion to the supporting element may be effected, for instance by forming this latter in three different pieces. For instance, in the case of the joint with constant angular velocity, the central piece is like 22 of FIG. 8, on which the triangular portions of the two annular elements are arranged and the further pieces are constituted by the other two elements, as 27 of FIG. 8, disposed each with respect to the central element.

The three elements 27, 22, 27 are then firmly connected to one another, for instance, by having holes communicating with one another and crossed by clamping bolts.

The invention is not limited to that which has been disclosed up to now, e.g., to the two supports, each provided with two opposite arms connected to each other by a quadrilateral polygonal system. For instance, according to a further embodiment, each support can be provided with three arms situated at 120°, and the system of tension rods is obtained again by starting from a flexible strip resistant to traction in the form of a sleeve and folded so as to obtain a hexagonal polygonal element.

This embodiment is shown schematically in FIG. 14. As there shown, in order to obtain a hexagonal polygonal system the triangular portion for the coupling with the supporting element is characterized by an angle at the vertex of 30°, instead of 45° as in the prveious example of quadrilateral element.

In this case, the six triangular portions are alternatively connected to the driving and driven supports so as to realize a three-arm arrangement at 120° on the driving support, coupled with an analogous three-arm arrangement at 120° on the driven support.

The present invention includes further solutions in which, for instance, one and the same joint comprises more than one strap.

In one embodiment, each of the polygon sides may be formed by a single strap, originally shaped according to an annular configuration and then disposed at the ends with the previously shown foldings. In this embodiment, the joint of FIG. 1 is constituted by four annular straps, instead of only one annular strap.

More generally, in this and in other embodiments, each side of the polygon is formed by a single annular strap.

Also in these embodiments, the furthermost parts of the strap are formed in a triangular shape in order to permit fitting the supports around the chamfer.

In fact, as is seen from what has been said above, the essential characteristic of the invention is determined by the presence of at least one strap that, before being mounted on the joint, has a tubular shape and then is connected to the arms of the supports so as to constitute branch connections, with some arms lying on a plane according to a regular polygonal arrangement; for instance, a quadrilateral as in FIG. 1 and 2, said plane coinciding with the ideal plane of separation of the two supports.

In this way of connection between the supports, it is possible to have both relative approaching movements and relative separating movements of said supports, and consequently of the relative shafts, as well as relative inclinations between the axes of the driving and driven shafts. In fact, considering the high flexibility of the strap 4, the branches a, b, c, d (FIG. 2) are connected to the ends of the arms by means of connections assimilable to hinges, with consequent possible rotations of the branches with respect to the supports, as it could happen, for instance, when the support 3 moves near the support 2 or also for instance, when the axis X--X is no longer aligned with the axis Y--Y.

Further, since the strap has per se a certain, even if modest or small extensibility, it is possible to have small relative parallel movements between the shafts and also small relative rotations of one shaft with respect to the other upon variations in the torque to be transmitted so as to absorb elastically the transients of load transmitted by one shaft to the other.

In particular, according to one possible embodiment of the invention, in order to increase the extensibility of the strap one may use reinforcing elements constituted by high twist nylon cords.

Therefore, owing to the cited characteristics, the joint of the invention is an elastic joint.

The joint according to the invention, with respect to the known elastic joints, has the advantage of not undergoing rubber hysteresis losses with consequent heating.

In fact, in the joint shown herein, the part adapted to bear the stresses to be transmitted between one support and the other is constituted by resistant and flexible elements in the form of cords of thin elements of high tensile strength polymeric material with reduced thicknesses, and consequently the hesteresis losses are practically negligible.

Further, the cost of the manufacturing process for the present joint is low and the joint is assembled in all its parts rapidly.

According to one advantageous solution, the supports may be provided in series, for instance through a molding operation, and then with simple tools it is possible to provide the holes to connect the various plates to one another and to block the tension rods on the supports.

Also, the connecting annular element for the transmission of motion between the supports may be obtained by means of a sleeve manufacturing process adapted for the simultaneous plurality of elements.

In fact, if the joint shown in the figures herein is examined, the outer development of the ring (FIG. 2) is determined by the formula:

    P=4×l+4×s

where:

l=the length of the branches between the ends of the supports;

s=the portion of the polygonal system, corresponding to the thickness of the support; and

P=the outer development of the polygonal system.

Once the torque to be transmitted between the two shafts and the length of the arms of the supports have been determined, as well as the width of the strap resistant section, it is possible to obtain rapidly from the geometrical figure of the joint the development of the polygonal system P. Said development P, as previously seen corresponds to the construction line of the thin strap in the form of a sleeve. When said sleeve has been defined, it is possible to proceed for the formation of a continuous tube to then realize a plurality of cuts perpendicular to the axis of the tube, with distance equal to the predetermined width S of the branches for the transmission of power in the joint.

Since the tube has an indefinite length and can be produced with manufacturing and vulcanizing systems according to known techniques, this permits one to realize on an industrial scale the essential element for the transmission of motion for a plurality of joints of one and the same type, or of different types on condition that with equal development the cut distance and the width of the annular elements are appropriately modified.

The invention is, of course, not limited to that which has been described up to now. According to another possible solution, the strap in the annular form may be manufactured with different materials. In the case in which it is necessary to have recourse to joints with elasticity or maximum torque different from one another, one may form tubes of the type previously described of polymeric material embedding cords of different type or differentily wound on the tube itself in order to modify the winding density.

To increase the inextensibility of the annular strap, one may use reinforcing cords of Kevlar or steel embedded in a layer of elastomeric material.

The annular strap may also be formed of a polymeric layer, for instance of elastomeric material, embedding a fabric of threads having the same resistance in weft and warp.

The fabric of threads having the same resistance in weft and warp, according to an alternative embodiment, may be embedded for instance in a polyurethane material or the like.

Also, according to a still further solution, when a high resistance to traction is required, said fabric may have the warp threads of a high resistance and the weft threads of a low resistance, for instance cotton threads.

The polymeric material, besides being elastomeric, may be formed of other plastic materials or homogeneous materials comprising plypropylene or nylon. In particular, in this case the tubular sleeves may be made of plastic materials, for instance nylon, stretched in circumferential direction.

The joint may be used in various fields of application and the application of the present joint in the automobile field is particularly advantageous, for instance, in place of the Cardan joint made of mechanical elements for the connection between the two forks.

The advantage of the use of the joint according to this invention in the automobile field is due to the high flexibility of the element of connection between the supports and to the ability of adapting itself to any oscillation of the vehicle.

According to further solutions, the joint of the present invention may be used, for instance, in the transmission of motion among mechanical devices in a computer.

Although some preferred embodiments according to the present invention have been described and illustrated, it is understood that the invention includes within its scope all the possible alternative embodiments accessible to a technician in the field; for instance, the tension rods of the polygon between the supports may be arranged substantially in a single plane, intending to indicate with the term "substantially" the possibility of the tension rods slightly moving away from said condition, for instance, for assuming the shapes of the edges of a frustum of a pyramid.

According to still other solutions, the tension rods of the joint may be made of a plurality of straps placed one over the other or by a number of annular straps equal to the number of the sides of the polygon.

The joint may also comprise oversize thicknesses of material at the connections to the rigid forks in order to reduce abrasion during operation.

Also, the principle of the invention comprises joints in which the sides of the polygon forming the tension rods are of a number greater than that described, e.g., of a quadrangular or a hexagonal polygon. In all the further solutions, the angles formed by the edges intended to constitute the triangular portion of the strap to be anchored to the supports will be less than those cited. These embodiments, with a greater number of sides, permit one to distribute high loads or forces on more than one tension rod. 

What is claimed is:
 1. A joint for transmission of motion from a driving shaft rotating around a first axis to a driven shaft rotating around a second axis, said joint comprising a driving support and a driven support associated with said shafts, each support comprising at least two arms, said joint further comprising at least one single element of connection between the arms for transmission of motion between the shafts constituted in the form of a closed annular strap of flexible material and resistant to traction, said strap being disposed substantially within a plane separating the two supports at a central position with respect to the joint so as to form a polygon whose vertices are the ends of the arms belonging alternatively to the driven and driving supports and whose sides constitute the tension rods for the transmission of motion between the driven shaft and the driving shaft, said tension rods during the operation being equal to half of the polygon sides, said strap comprising alternatively a pair of opposite sides under traction and a pair of opposite inactive sides and the traction condition exchanging with the inactivity condition on varying the sign of the transmitted torque, said strap, at each end of the arm to which it is connected, being folded upon itself with superimposition of two sides thereof to form a first edge directed transversely with respect to the width of the strap, said two sides rotating with respect to the superimposition on the arm around a second edge, so as to form a triangle, said second edge forming an angle α of inclination predetermined with respect to the first edge, said two sides projecting from the superimposition to the ends of the arms forming the tension rods lying on a single plane, said two sides superimposed on said arms and forming in the support said first and second edges surrounding a chamfer of corresponding shape and being provided with two rigid elements associated and fixed with blocking means for blocking with respect to said chamfer of the support, said blocking means extending beyond an extent of the annular strip around the chamfer.
 2. A joint as in claim 1, characterized in that said annular strap is formed of a sleeve of flexible polymeric material and resistant to traction through two contiguous cuts on planes perpendicular to the axis of the tube.
 3. A joint as in claim 1 or 2, characterized in that said annular strap is in the form of rings of elastomeric material embedding reinforcements adapted to withstand the tensile forces in a direction parallel to the edges of the ring.
 4. A joint as in claim 1 or 2, characterized in that said annular strap comprises means to absorb elastically variations of torques between the two shafts.
 5. A joint as in claim 1, wherein said joint transmits constant angular velocity between the said two driving and driving shafts.
 6. A joint as in claim 5, wherein said driving and driven supports comprise end supports whose middle sections are on one and the same first plane, and wherein an intermediate support is disposed between the two end supports lying on a second plane whose middle section is perpendicular to the first plane, said intermediate support forming a rigid element of connection between the two equal joints, each of which comprises a polygonal system of sides lying on said first plane.
 7. A joint as in claim 1, characterized in comprising means for avoiding mechanical interferences between the central portions of the two supports in the presence of relative approaching movements between said two shafts.
 8. A joint for transmission of motion from a driving shaft rotating around a first axis to a driven shaft rotating around a second axis, said joint comprising a driving support and a driven support associated with said shafts, each support comprising at least two arms, said joint further comprising connection means positioned between said arms for transmission of motion between the shafts constituted in the form of a plurality of individual closed annular straps of flexible material and resistant to traction, said straps being disposed substantially within a plane separating the two supports at a central position with respect to the joint so as to form a polygon whose vertices are the ends of the arms belonging alternatively to the driven and driving supports and whose sides constitute the tension rods for the transmission of motion between the driven shaft and driving shaft, each side of said polygon being formed of a single one of said straps, said tension rods during the operation being equal to half of the polygon sides, said strap comprising alternatively a pair of opposite sides under traction and a pair of opposite inactive sides and the traction condition exchanging with the inactivity condition on varying the sign of the transmitted torque, said strap, at each end of the arm to which it is connected, being folded upon itself with superimposition of two sides thereof to form a first edge directed transversely with respect to the width of the strap, said two sides rotating with respect to the superimposition on the arm around a second edge, so as to form a triangle, said second edge forming an angle α of inclination pre-determined with respect to the first edge, said two sides projecting from the superimposition to the ends of the arms forming the tension rods lying on a single plane, said two sides superimposed on said arms and forming in the support said first and second edges surrounding a chamfer of corresponding shape and being provided with two rigid elements associated and fixed with blocking means for blocking with respect to said chamfer of the support, said blocking means extending beyond an extent of the annular strip around the chamfer. 